The tracheobronchial epithelium (TBE) is the respiratory compartment that is maintained by the basal cell progenitor. Basal cell progenitor proliferation and differentiation are critical components of lung health and changes in these functions contribute to respiratory disease. We suggest that treatments which normalize basal cell progenitor functions can be used to heal the TBE. To achieve this goal, we must identify the signals that regulate TBE basal cell functions. This proposal is designed to resolve the issues that prevent modeling of human TBE basal cells in mice and use of genetically-modified mice to test signaling pathway function in vivo. We and others have shown that there are subsets of human and mouse TBE basal cells and that TBE basal cells are different from basal cells that maintain non-respiratory tissues. Thus, we hypothesize that: Tracheobronchial basal cells are defined by a unique gene expression signature. Aim 1: Determine the gene expression profile of human and mouse TBE basal cells. Sub-hypothesis: TBE basal cell subtypes exhibit a characteristic gene expression signature. We will use gene expression profiling (GEP) to determine if: 1) the normal human and mouse TBE is populated by molecularly-distinct subsets of basal cells; and 2) there are analogous human and mouse TBE basal cell subsets. Aim 2: Identify TBE basal cell-specific genes. Sub-hypothesis: TBE basal cells are a molecularly-distinct tissue-specific basal cell subtype. We will use GEP to determine if the mouse TBE basal cell transcriptome contains a signature that is distinct from basal cells in other tissues. We will then use quantitative reverse transcription polymerase chain reaction (qRT-PCR) and in situ hybridization analysis to identify a gene(s) that is unique to the TBE basal cell and its putative subtypes. In the future, we will create a new genetic model(s) that uses a TBE basal cell-specific promoter to modify gene expression in the mouse TBE basal cell subtype(s) that is analogous to the human TBE basal cell subtype(s). This cell type-specific approach will prevent the non-respiratory, life-threatening genetic modifications that currently confound in vivo analysis of signaling in TBE basal cells.